Saudi Arabian shares retreated the most in more than three months, leading declines in the Middle East amid investor concern that Arab nations may be at risk of retaliatory attacks by Islamic State militants.

Saudi Arabia is a target for both sides in Iraq’s deepening conflict, one reason it has ramped up security levels to confront a threat that’s more immediate than the Arab Spring revolts three years ago.

U.S. officials planning potential military strikes on Syria aren’t limited to a one-day operation, an administration official said, as the UN Security Council’s permanent members considered a resolution condemning last week’s suspected chemical attack.